signalling and call processing

7/28/2019 Signalling and Call Processing

1/23

Signalling And CallProcessing


2/23

GSM Functional Planes

OAM

CM

MM

RR

transmission

operator user

CM

MM

RR

trans

MS BTS BSC MSC/

VLR

HLR

GMSC

BTS BSCMSC

VLRHLR GMSC


3/23

gna ng ro ocoArchitecture

BSSAP

MM

CM

BSSAP

CM

BTS

MS BSC MSC

AUm Abis B/C/D/E/F

MTP

SCCP

MTP

SCCPSCCP

MM

RRM

RRM

RRM

LAPDLAPDLAPDmLAPDmSignaling

Layer1

Signaling

Layer1

Signaling

Layer1

Signaling

Layer1

BTSM BTSM

I

S

U

P

M

A

P

TCAP

Relay

MTP


4/23

y Signaling View

VLR

VLR

MAP/G

MAP/BMAP/C

MAP/

D

MAP

MAP/F

MAP/E / ISUP

EIR

MAP /

ISUP

MAP /

ISUP

MSC

BSC

BTS

MS

PSTN/

ISDN

PLMN

BSSAP /

Q.931

BSS

LAPD / Q.931

LAPDm / Q.931

MSC

HLR AUC


5/23

What Are RRM Functions?

RRM functions cover all activities relatedto physical layer (air interface)

These relate functions like

Channel assignment

Channel release

Channel change and handover

Change of channel frequencies, hoppingsequences (algorithms) and frequency tables

Measurement reports from the MS

Power control and Time Advance

Modification of channel modes (speech and


6/23

Some RRM Messages

Name of Message Sent by &

sent to

Carried on

Channel

Purpose of Message

Assignment

Command

BSC to MS SDCCH Allocation of TCH

(ARFCN & TS#)

Assignment

Complete

MS to BSC SDCCH Acknowledge for

Assignment Command

Channel Request MS to BSC RACH Request for channel

Channel Release BSC to MS SDCCH orTCH

Release of SDCCH orTCH

Cipher Mode

Command

BSC to MS SDCCH To indicate to MS that

ciphering will start


7/23

Some RRM Messages (Contd.)Name of Message Sent by &

sent to

Carried on

Channel

Purpose of Message

Cipher Mode

Complete

MS to BSC SDCCH Acknowledge that MS

will also start ciphering

Immediate

Assignment

Command

BSC to MS AGCH Allocation of TCH

(ARFCN & TS#)

Paging Request BSC to MS PCH To inform MS about

incoming call / SMS

Paging Response MS to BSC SDCCH To respond to paging by

revealing MS identity(TMSI)

System Information

Messages

BSC to all

MSs

BCCH To broadcast CGI,

System information,

neighbouring cell

description


8/23

Some RRM Messages (Contd.)

Name of Message Sent by &sent to Carried onChannel Purpose of Message

Measurement

Report

MS to BSC SACCH MS reporting on signal

strength measurement

Handover

Command

BSC to MS FACCH /

SACCH

Change of MS channel

allocation (will includenew ARFCN & TS#)

Handover Access MS to BSC

(new)

FACCH /

SACCH

Initial message sent on

the new TCH about

presence of MS

HandoverComplete

MS to BSC(new)

FACCH /SACCH

MS informs new BSCthat handover has been

completed

Handover Failure MS to BSC

(old)

SACCH /

FACCH

MS indicates that

handover has failed


9/23

What Are MM Functions?

All activities connected with mobility ofMS are MM functions

Location updating

Periodic registration

Authentication procedure

IMSI attach procedure (on power up a MS

will present its IMSI to network and get aTMSI)

IMSI detach ( on power off of a MS, detachprocedure to tell network it is no longer in

service.


10/23

Some MM Messages

Name of Message Sent by &sent to Carried onChannel Purpose of Message

Authentication

Request

MSC to MS SDCCH Sending RAND for

authenticating MS

Authentication

Response

MS to MSC SDCCH MS response by sending

SRES

Authentication

Reject

MSC to MS SDCCH MSC informing MS that

authentication has failed

Location Updating

Request

MS to MSC SDCCH To update location by

including TMSI and LAI

Location Update

Accept Command

MSC to MS SDCCH To indicate that location

updating has been done


11/23

Some MM Messages (Contd.)Name of

Message

Sent by &

sent to

Carried on

Channel

Purpose of Message

TMSI

Reallocation

Command

MSC to MS SDCCH To indicate that location

updating has been done and

will include new TMSI

TMSI

ReallocationComplete

MS to MSC SDCCH Acknowledgement of TMSI

Reallocation Command byMS

IMSI Detach

Indication

MS to MSC SDCCH Indication to MSC that its

identity be removed from

MSC/VLR

IMSI AttachCommand

MS to MSC SDCCH To inform MSC that MS isagain powered up

Identity

Request

MSC to MS SDCCH MSC requesting MS to send

its identity (IMSI)

Identity

Response

MS to MSC SDCCH MS sends its identity (IMSI)


12/23

What are CM Functions?

CM functions relate to establishing,releasing call and status indication

Call establishment for mobile-originatedcalls

Call establishment for mobile-terminatedcalls

Indication of status

Changes of transmission mode during anongoing call

Call reestablishment after interruption of an


13/23

Flow of CM Messages

MSC /GMSC

PSTN /PLMN

MS A

NNI

ISUP messages

UNI

Q.931 messages

Interface between MS and MSC is called User toNetwork Interface (UNI)

Q.931 messages are used in this interface

Interface between MSC / GMSC and externalnetwork is called Network to Network Interface

(NNI)ISUP messages are used in this interface


14/23

Message name

Starting a call

Transmitted by

SETUPEMERGENCY SETUP

CALL PROCEEDING

PROGRESS

CALL CONFIRMED

ALERTING

CONNECT

MS/MSCMS

MSC

MSC

MS

MS/MSC

MS/MSC

During a call

START DTMF

STOP DTMF

MODIFY

USER INFORMATION

MS

MS

MS/MSC

MS/MSC

Ending a call

DISCONNECT

RELEASE

RELEASE COMPLET

MS/MSC

MS/MSC

MS/MSC

Abnormal conditions

STATUS

STATUS ENQUIRYCONGESTION CONROL

MS/MSC

MS/MSCMS/MSC

Call Management Messages


15/23

Important ISUP Messages

There are 3 important ISDN User Part(ISUP) messages

IAM (Initial Address Message) is sent by the

calling network to initiate a call sendingcomplete information about the call callingnumber, called number, type of call and otherinformation

ACM (Address Complete Message) is sent byterminating network to confirm that the callednumber is free and is being alerted

ANM (ANswer with Metering) is sent by

terminating network once the called


16/23

Important Q.931 Messages

There are 3 important ISDN User Part

(ISUP) messages

Setup message is sent by user or network

(originating side) to initiate a call by sendinginformation about the call calling number,

called number, type of call and other

information this is equivalent to IAM

Alerting is sent by the other side (terminating

side) to confirm that the called number is free

and is being alerted this is equivalent to

ACM


17/23

Mobile Originated Call

MS BSC MSC VLR PSTN

Setup (dialled digits + encryption)

Assignment of TCH (SDCCH)

Assignment Complete

Assignment Complete

(voice path from MS to MSC)

Assignment of trunk

on A channel

Call Proceed (on SDCCH)

Send info for Outgoing Call(call restriction query)l

Alerting

Connect

Connect Acknowledge

Complete Call

Route Establishment

Answer

1

2

3

4

5

6

7

8

9

10

11

12

13

14

ringback heard by MS

Call Establishment to PSTN no. (IAM)

(ACM)

(ANM)

M I M bil


18/23

Messages In Mobile

Originated Call1. When user dials the number and presses ok button MS sends Setup

message transferring this info to MSC2. MSC sends a message to VLR for accessing subscription information

of MS

3. VLR checks the database of MS to determine whether the call can beallowed or not and returns a message

4. MSC send Call Proceedingmessage to MS5. MSC allocates a trunk between BSC &MSC and asks BSC to assign

TCH for MS

6. BSC allocates TCH, sends Ass ignmentmessage to MS

7. MS tunes to the TCH and sends Ass ignment Completemessage toBSC

essages n o e r g na e


19/23

essages n o e r g na eCall

8. BSC deallocates SDCCH, connects TCH to the trunk

and sends Ass ignment Completemessage to MSC9. MSC sends Initial Address Message (IAM) to PSTN

containing the digits dialed

10. PSTN sets up the call and returns Address Complete

Message(ACM)11. MSC informs MS that destination number is being

alerted, subscriber hears ringing tone

12. When called subscriber answers PSTN sends Answer

message13. MSC informs MS that connection has been established

through the Connectmessage

14. MS returns a Connect Ack now ledgemessage and

conversation can proceed


20/23

Page Request (TMSI)

Alerting

Call Confirmed

Page Message to

appropriate BSCs

Setup

Connect

Connect Acknowledge

Setup Complete

Answer

Channel Request (on RACH)

SDCCH Assignment (on AGCH)

Page Response on SDCCHPage Response

Process Access Request

Complete Call

Page

LA & TMSI

Send info for Incoming Call

Routing Information

Send Routing Information (VLR)12

3

4

5

6

7

8

9

10

11

12

13

14

15

1617

18

1920

21

MS BSC VLR PSTNHLR

end of MSC-VLR

dialogue

Call Establishment Message

Mobile Terminated Call

MSC

GMSC

(IAM)

(ACM)

(ANM)

M I M bil


21/23

Messages In Mobile

Terminated Call

1. GMSC receives IAMfor an incoming call from PSTN to MS withdirectory no MSISDN

2. MSC requests routing information from HLR through RoutingInformation Message by including MSISDN

3. HLR acknowledges by returning MSRN / MSISDN and address ofserving VLR

4. MSC queries VLR with Send Info fo r Incom ing Cal lmessage

5. VLR responds with a Pagemessage that specifies the LAI & TMSI ofMS

If incoming calls are barred VLR will inform the MSC and MSCwould connect to an appropriate announcement


22/23

Call (Contd.)

6. MSC determines the BSCs covering LAI and

sends the Pagemessage to each of theBSCs

7. Each BSC broadcasts TMSI of MS in Page

Requestmessage in PCH8. MS responds with Channel Request

message in RACH

9. BSC allocates SDCCH, sends ChannelAss ignmentmessage to MS over AGCH

10.MS sends Page Responsemessage

(containing MSs TMSI & LAI) over SDCCH

essages n o e erm na e


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essages n o e erm na eCall (Contd.)13.VLR responds with a Complete Call

message14.MSC sends Setupmessage to MS

15.MS responds with Call Con firmed

message16.MS sends Alert ingmessage to MSCindicating the subscriber is being alertedabout incoming call

17.MSC returns ACMto PSTN

18.When user answers, MS sends Connectmessage to MSC

19 MSC returns Connect Acknow ledge

signalling and call processing

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